Fuel, fuel additives and various chemicals used in the petrochemical industry are derived from oil, gas and coal, all finite sources. Biomass, on the other hand, is considered a renewable source. Biomass is biological material (including biodegradable wastes) which can be used for the production of fuels or for industrial production of e.g. fibres, chemicals or heat. It excludes organic material which has been transformed by geological processes into substances such as coal or petroleum.
Production of biomass derived products for non-food applications is a growing industry. Bio-based fuels are an example of an application with strong growing interest. Biomass contains sugars (hexoses and pentoses) that may be converted into value added products. Current biofuel activities from sugars are mainly directed towards the fermentation of sucrose or glucose into ethanol or via complete breakdown via Syngas to synthetic liquid fuels. EP 0641 854 describes the use of fuel compositions comprising of hydrocarbons and/or vegetable oil derivatives containing at least one glycerol ether to reduce particulate matter emissions.
More recently, the acid catalysed reaction of fructose has been re-visited, creating HMF as an intermediate of great interest. Most processes investigated have the disadvantage that HMF is not very stable at the reaction conditions required for its formation. Fast removal from the water-phase containing the sugar starting material and the acid catalyst has been viewed as a solution for this problem. Researchers at the University of Wisconsin-Madison have developed a process to make HMF from fructose. HMF can be converted into monomers for plastics, petroleum or fuel extenders, or even into fuel itself. The process by prof. James Dumesic and co-workers first dehydrates the fructose in an aqueous phase with the use of an acid catalyst (hydrochloric acid or an acidic ion-exchange resin). Salt is added to salt-out the HMF into the extracting phase. The extracting phase uses an inert organic solvent that favors extraction of HMF from the aqueous phase. The two-phase process operates at high fructose concentrations (10 to 50 wt %), achieves high yields (80% HMF selectivity at 90% fructose conversion), and delivers HMF in a separation-friendly solvent (DUMESIC, James A, et al. “Phase modifiers promote efficient production of Hydroxymethylfurfural from fructose”. Science. 30 Jun. 2006, vol. 312, no. 5782, p. 1933-1937). Although the HMF yields from this process are interesting, the multi-solvent process has cost-disadvantages due to the relatively complex plant design and because of the less than ideal yields when cheaper and less reactive hexoses than fructose, such as glucose or sucrose, are used as a starting material. HMF is a solid at room temperature which has to be converted in subsequent steps to useful products. Dumesic has reported an integrated hydrogenolysis process step to convert HMF into dimethylfuran (DMF), which is assumed to be an interesting gasoline additive.
In WO 2006/063220 a method is provided for converting fructose into 5-ethoxymethylfurfural (EMF) at 60° C., using an acid catalyst either in batch during 24 hours or continuously via column elution during 17 hours. Applications of EMF were not discussed. Also in copending patent application PCT/EP2007/002145 the manufacture of HMF ethers are described, including the use of such ethers as fuel or fuel additive. Indeed, both the methyl ether and the ethyl ether (methoxymethylfurfural, or MMF; ethoxyethylfurfural or EMF) were prepared and tested. A similar case is co-pending patent application PCT/EP2007/002146, which describes the manufacture of HMF esters, such as acetylmethylfurfural (AMF).
Moreover, it is known to make furfural from the polysaccharide hemicellulose, a polymer of sugars containing five carbon atoms each. When heated with sulphuric acid, hemicellulose undergoes hydrolysis to yield these sugars, principally xylose. Under the same conditions of heat and acid, xylose and other five carbon sugars undergo dehydration, losing three water molecules to become furfural:C5H10O5→C5H4O2+3H2O
Although MMF, EMF, AMF and other ethers and esters of HMF and furfural are useful as fuel or fuel additives, the inventors found that these ethers and esters leave room for improvement, in particular when used in higher concentration blends with fuels such as gasoline, kerosene, diesel, biodiesel or green diesel. The inventors have therefore set out to overcome this shortfall. It is known that HMF may be converted into 2,5-dimethylfuran. For instance, in “Production of dimethylfuran for liquid fuels from biomass-derived carbohydrates”, Nature, vol. 447 (21 Jun. 2007), pp. 982-985, James Dumesic et al. describes the conversion of fructose into HMF, which is subsequently converted into several hydrogenation steps via 2,5-dihydroxymethylfuran and 2-methyl-5-hydroxymethylfuran into DMF. Thus, a large amount of hydrogen is required to generate a liquid fuel suitable for the transportation sector.
Surprisingly, the current inventors found that the conversion of HMF into DMF is not required in order to prepare a product with a high energy density, suitable boiling point and suitable solubility. Moreover, suitable fuel or fuel additives may even be made from furfural, HMF, HMF ethers and HMF esters such as EMF and AMF and/or mixtures containing these components with much smaller amounts of hydrogen and without losing molecular mass but with adding molecular mass to the products. This would therefore provide a route to an alternative fuel or fuel additive from a renewable (and hence CO2 neutral) source.